A STYLEREF field's result runs are the chapter a reader shows before it
repaginates. The DOCX import dropped them and set the field's text empty, so a
header saved as .docx came back with a blank running head. ODF kept it.
Found by comparing the header and footer zones on a round trip, which nothing
did — they are documents of their own and hold what only they can. The corpus
gains two legs besides: a second save, and Word's dialect on its way out as ODT.